Dog-clutch coupling device

ABSTRACT

The invention relates to a device for coupling two shafts that are intended to rotate in the continuation of one another with respect to a casing ( 4 ). A dog clutch couples the two shafts. 
     The device comprises clutch-release means allowing the dog clutch ( 9 ) to be uncoupled. According to the invention, the clutch-release means comprise a ramp ( 17 ) secured to the casing ( 4 ), the ramp ( 17 ) having a helical shape around the axis ( 1 ), a flat disk ( 19 ) secured to the first shaft ( 3 ) the plane of which is more or less perpendicular to the axis ( 1 ), an element ( 20 ) intended to roll between the ramp ( 17 ) and the disk ( 19 ) so as to cause a translational movement of the first shaft ( 3 ) with respect to the casing ( 4 ) more or less along the axis ( 1 ), the translational movement allowing the dog clutch ( 9 ) to be uncoupled. 
     The specific structure of the clutch-release means enables the shafts to be uncoupled while they are in rotation.

The invention relates to a device for coupling two shafts that areintended to rotate in the continuation of one another. A dog clutchcouples the two shafts. A dog clutch generally comprises teeth orprotrusions belonging to each of the two shafts. When the teeth (orprotrusions) collaborate with one another, the two shafts are coupled. Adog-clutch coupling device also comprises means for separating the teethof each shaft in order to uncouple them. These means will be termedclutch-release means in the remainder of the description.

Known clutch-release means entail halting the rotation of the two shaftsand applying an external force to separate the teeth. What happens isthat the teeth are generally kept in contact by means of a spring and itis therefore necessary to overcome the force of this spring in order torelease the clutch.

The object of the invention is to alleviate these difficulties byproposing a dog-clutch coupling device in which the clutch-release meanscan uncouple the shafts even while these are rotating. Allowinguncoupling during rotation makes it possible to use the clutch-releasemeans as a safety member. They allow rapid uncoupling without having towait for rotation to stop.

To this end, the subject of the invention is a device for coupling twoshafts that are intended to rotate with respect to a casing, in thecontinuation of one another more or less about an axis, the devicecomprising a dog clutch allowing one of the shafts to drive the otherand clutch-release means allowing the dog clutch to be uncoupled,characterized in that the clutch-release means comprise a ramp securedto the casing, the ramp having a helical shape around the axis, a flatdisk secured to the first shaft the plane of which is more or lessperpendicular to the axis, an element intended to roll between the rampand the disk so as to cause a translational movement of the first shaftwith respect to the casing more or less along the axis, thetranslational movement allowing the dog clutch to be uncoupled.

The invention furthermore makes it possible to considerably reduce theforce needed for clutch release. By virtue of the invention, the forceneeded to separate the teeth of the dog clutch is provided not by meansexternal to the device but by the device itself and, more specifically,by the rotational energy of the shafts. The only force needed for clutchrelease is, by virtue of the invention, a force to move the ball from aposition of rest to a position between the ramp and the disk.

The invention will be better understood and other advantages will becomeapparent from reading the detailed description of one embodiment of theinvention, this description being illustrated by the attached drawing inwhich:

FIGS. 1, 2 and 3 depict a coupling device according to the invention inthe clutch-engaged position;

FIGS. 4, 5 and 6 depict the same device during the start of clutchrelease;

FIGS. 7, 8 and 9 once again depict the same device during clutchrelease;

FIGS. 10, 11 and 12 depict the device at the end of clutch release;

FIGS. 13, 14 and 15 depict the device in a clutch-released position;

FIGS. 1, 4, 7, 10 and 13 depict the device in section, the plane ofsection containing the axis of rotation of the shafts;

FIGS. 2, 5, 8 and 11 depict the device in section, the plane of sectionbeing perpendicular to the axis of rotation of the shafts, the positionof the plane of section in FIGS. 2, 5, 8 and 11 being shown in FIGS. 1,4, 7 and 10 by a fine chain line the ends of which each bear an arrowand a reference label A;

FIGS. 16 and 17 depict a thermal cut-out controlling the clutch release;

FIG. 18 depicts an exemplary embodiment of the teeth of the dog clutch.

To simplify the remainder of the description, the same elements willbear the same references in the various figures.

In FIG. 1, a coupling device is depicted in section on a planecontaining an axis 1 about which two shafts 2 and 3 can rotate withrespect to a casing 4. The shaft 3 for example is that of the rotor ofan electric motor. Stator windings 5 of the motor are secured to thecasing 4 and rotor windings 6 are secured to the shaft 3. A rotatingbearing comprising, for example, a rolling bearing 7 allows the shaft 3to rotate with respect to the casing 4, rotation being about the axis 1.The shaft 2 for example allows the electric motor to be coupled to arelay box (not depicted) via splines 8.

A dog clutch 9 allows the shafts 2 and 3 to be coupled and uncoupled. Inthe example depicted, the dog clutch 9 comprises a first series of teeth10 secured to the shaft 2 and a second series of teeth 11 secured to oneend 12 of the shaft 3. The end 12 can move in terms of translation alongthe axis 1 with respect to the shaft 3. A rotational connection of theend 12 about the axis 1 with respect to the shaft 3 is provided by meansof splines 13. The teeth 10 and the teeth 11 collaborate with oneanother to allow the shaft 2 to be driven by the shaft 3 when thecoupling device is in the clutch-engaged position. Of course theinvention is not limited to the driving of the shaft 2 by the shaft 3.The opposite is also possible for example if the electric motor is usedin electric current generator mode.

A helical spring 14 tends to keep the teeth 10 and 11 in contact. Thespring 14 bears at its first end 15 against the shaft 3 and at itssecond end 16 against the end 12. When the teeth 11 and 12 are incontact, the coupling device is in the clutch-engaged position.

Clutch-release means allow the dog clutch 9 to be uncoupled. Morespecifically, these means allow the teeth 10 to be separated from theteeth 11 to obtain a clutch-released position for the coupling device.

The clutch-released position will be described later on with the aid ofFIGS. 13 to 15. To move the teeth 10 away from the teeth 11, the clutchrelease means compress the spring 14 by performing a translationalmovement of the end 12 with respect to the shaft 3.

According to the invention, the clutch-release means comprise a ramp 17with a helical shape about the axis 1. The ramp 17 is secured to thecasing 4. The ramp 17 is for example fixed to the casing 4 by screws 18.The clutch-release means also comprise a flat disk 19 secured to theshaft 3 or more specifically to its end 12. The clutch-release meansalso comprise an element, for example a ball 20, intended to rollbetween the ramp 17 and the disk 19 so as to cause the translationalmovement of the end 12 of the shaft 3 with respect to the casing 4 moreor less along the axis 1. The shape of the ramp 17 is dependent on theshape of the element rolling along it. More specifically, when theelement is a ball 20, the ramp 17 has the shape of a channel section inwhich the ball 20 can roll. Two sections of the ramp 17 are visible inFIG. 1 and are in the shape of a U. For the remainder of thedescription, the term ball 20 will be used to denote the element. Ofcourse, this term does not restrict the invention to a sphericalelement. The invention can be embodied for other shapes of element suchas, for example, a cylindrical or tapered roller. The shape of theelement needs to be chosen so that it can roll between the ramp 17 andthe disk 19, and the shape of the ramp needs to be tailored accordinglyin order to able to guide said element.

Furthermore, the shape of the ramp 17 allows the ball 20 to make onerevolution about the axis 1 during the clutch-release operation. For abetter view of the shape of the ramp 17, reference is made to FIG. 2which depicts the device already described in FIG. 1, in the plane ofsection AA perpendicular to the plane of FIG. 1. In FIG. 2, the ramp 17can be seen as a circle centered on the axis 1.

FIG. 3 depicts, in a clutch-engaged position, the clutch-release meansin a developed view. More specifically, the ramp 17 is projected onto acylinder of circular base of axis 1. The cylinder is then opened outflat in the plane of FIG. 3. It is thus possible to see in this figurethe helix angle 21 of the ramp 17 with respect to the disk 19 which ismore or less perpendicular to the axis 1. The method of depiction as adeveloped view will be used again for FIGS. 6, 9, 12 and 15.

FIG. 3 also shows means 22 for keeping the ball 20 pressed against theramp 17 when the coupling device is in the clutch-engaged position.Advantageously, the means 22 ensure that there is a functional clearance23 between the ball 20 and the disk 19 in the clutch-engaged position.The functional clearance is better visible in an enlarged part view 24,this part view being centered around the ball 20 and also shown in FIG.3. This functional clearance 23 makes it possible to avoid the ballrubbing against the disk 19 when the coupling device is in theclutch-engaged position. Specifically, as the ramp 17 is secured to thecasing 4 and the disk 19 is secured to the shaft 3, a relative movementof the disk 19 with respect to the ramp 17, which exists in theclutch-engaged position when the shaft 3 is rotating about the axis 1,would lead to friction and, ultimately, to wear of the ball 20 if thefunctional clearance 23 were not present.

The means 22 have, for example, the shape of a fork which, in theclutch-engaged position, prevents the ball 20 from rolling along theramp 17.

At the start of clutch release, which position is visible in FIGS. 4, 5and 6, the fork, or more generally the means 22, move the ball 20 tobring it into contact both with the disk 19 and with the ramp 17. Tosimplify the remainder of the description, the fork will bear thetopological reference 22. However, it must be clearly understood thatthe means 22 are not restricted to a component in the shape of a fork.

When the ball 20 has left the hollow 24 in which it lay during theclutch-engaged position, it finds itself in contact both with the ramp17 and with the disk 19. The rotation of the disk 19 with respect to theramp 17 drives the ball 20 between the disk 19 and the ramp 17. Aposition in which the ball 20 rolls between the disk 19 and the ramp 17is depicted in FIGS. 7, 8 and 9. The rotation of the ball 20 thereforeseparates the disk 19 from the ramp 17. This is a translational movementalong the axis 1. This movement forces the teeth 10 and 11 apart. Theposition depicted in FIGS. 7 to 9 is fleeting, in which position theball 20 rolls between the disk 19 and the ramp 17 without stopping.

The materials of the ramp 17, of the disk 19 and of the ball 20, and thehelix angle 21, are chosen so that the ball 20 rolls without slippingbetween the ramp 17 and the disk 19. More specifically, the coefficientsof friction between, on the one hand, the ball 20 and the ramp 17 and,on the other hand, the ball 20 and the disk 19, need to be very muchgreater than the helix angle 21. The coefficient of friction between twomaterials is defined as the minimum angle of inclination that thedirection of a force exerted on a first component made of one of thematerials, which component is placed on a second component made of theother material, adopts such that the first component can slide withrespect to the second. Values of coefficients of friction for pairs ofmaterials are commonly found in the literature, these values beingdefined by the tangent of the minimum angle of inclination.

In FIG. 9, which is a developed view, the direction of travel of theball 20 is embodied by the arrow 25.

FIGS. 10, 11 and 12 depict the device at the end of clutch release. Theball 20 has finished its travel along the ramp 17 and has been halted inits path by a stop 26 comprising a contact region 27 intended toaccommodate the ball 20. Advantageously, the contact region 27 is moreor less in the shape of a portion of a hollow sphere of the samediameter as the ball 20 so as to spread the force of contact between theball 20 and the stop 26 and thus avoid any damage to the stop 26 or tothe ball 20. If, as a replacement for the ball 20, use is made of anelement that does not have a spherical shape, the shape of the contactregion 27 of the stop will of course be halted accordingly. Indeed,clutch release can be done when the shafts 2 and 3 are rotating. Theball 20 travels over the entirety of the ramp 17 when the shaft 3 makestwo revolutions about the axis 1. In consequence, the higher therotational speed of the shaft 3, the faster the ball 20 will accomplishits travel and, accordingly, the more violent the impact between thestop 26 and the ball 20 will be. The material and dimensions of the stop26 and of the ball 20 are therefore chosen according to the maximumrotational speed of the shaft 3, at which speed a clutch-releaseoperation is permitted.

In the position depicted in FIGS. 10, 11 and 12, the ball 20 hascompleted its travel against the stop 26 but has not yet reached itsposition of rest in the clutch-released position. There remains aclearance 28 between the fork 22 and the ball 20 or, more specifically,between a slightly recessed housing 28 made in the fork 22. The positiondepicted in FIGS. 10, 11 and 12 is short-lived because the spring 14tends to push the disk back toward the ramp 17. The ball 20 is thereforepushed back into the housing 29 of the fork 22. This position of theball 20 corresponds to the clutch-released position of the device, whichposition is depicted in FIGS. 13, 14 and 15. In this position, the teeth10 secured to the shaft 2 and the teeth 11 secured to the shaft 3 areuncoupled and clutch release has effect. More specifically, the shaft 2and the shaft 3 can rotate independently of one another about the axis1.

Advantageously, the shape of the ramp 17 allows the ball 20 to make arotation of about one revolution about the axis 1 during theclutch-release operation. This revolution can easily be seen bycomparing FIGS. 2 and 14. FIG. 2 depicts the device in theclutch-engaged position and FIG. 14 in the clutch-released position. Inthese two figures, the ball 20 has more or less the same angularposition about the axis 1. Between these two positions, the ball 20 hasmore or less made one revolution about the axis 1. This more or lessidentical angular position about the axis 1 between these two positionsallows the device to engage in a simple way. Clutch engagement consistsin moving from the clutch-released position to the clutch-engagedposition.

To engage the clutch, all that is required is for the fork 22 to pivotin order thus to cause the ball 20 to drop into the housing 24 of theramp 17. The pivoting of the fork 22 is about an axis 30 secant with theaxis 1. In the clutch-release position, the axis 30 passes through theball 20 more or less at its center. The pivoting of the fork 22 can alsobe seen in the developed FIGS. 3, 6, 9 and 12. Indeed, in these figures,the axis 30 is more or less perpendicular to the plane of the figures.Between the clutch-engaged position and the clutch-release position, thefork 22 has more or less effected a quarter of a revolution about theaxis 30. In the clutch-release position visible in FIG. 15, theleft-hand part 22 a of the fork, in which part the housing 29 is made,is situated more or less in the continuation of the ramp 17 in thedirection in which the ball 20 moves when it reaches the clutch-releaseposition.

Control of the pivoting of the fork may be electromagnetic for example,by means of a winding 31 and 32 visible in FIG. 2. To ensure that thedevice is suitably safe, the fork 22 may be in the clutch-engagedposition when an electric current is passing through the windings 31 and32. In the absence of electric current in the windings 31 and 32, thefork 22 pivots to reach its clutch-release position. Thus, a failure inthe power supply will immediately lead to the clutch-release of thedevice.

FIGS. 16 and 17 depict means of controlling the fork 22 in a view fromabove perpendicular to the axis 30. Magnetic circuits 33 and 34 passthrough the windings 31 and 32. The magnetic circuits 33 and 34, and thewindings 31 and 32, form a fixed part or stator of electromagneticcontrol means for controlling the fork 22. A moving part 35 can pivotabout the axis 30 and, secured to the fork 22, forms the rotor of theelectromagnetic control means for controlling the fork 22.

To further increase the safety of the coupling device, the fork mayadvantageously be controlled by a thermal cut-out 36. More specifically,when the temperature within the device exceeds a given value, thethermal cut-out 36 cuts out and causes the fork 22 to rotate for exampleby exerting a force on a finger 37 secured to the fork 22. The finger 37is for example arranged on the fork 22 or on the moving part 35 in sucha way that the force exerted by the thermal cut-out 36 generates enoughof a moment to cause the fork 22 to pivot about the axis 30.

FIG. 16 depicts the rotor 35 and the thermal cut-out 36 in theclutch-engaged position. FIG. 17 depicts the thermal cut-out 36 after ithas been triggered and shows the corresponding position of the rotor 36.

The thermal cut-out 36 comprises for example a sleeve 38 secured to thecasing 4. Inside the sleeve 38, a piston 39 can move in terms oftranslation along an axis 40 to exert the force that causes the fork 22to pivot. In the position depicted in FIG. 16, one or more springs, inthis instance two coaxial springs 41 and 42, are compressed between thepiston 39 and the sleeve 38. A ball 43 locks the relative position ofthe piston 39 with respect to the sleeve 38. A cam 44 holds the ball 43in this position. A fusible element 45 blocks the cam 44. When thefusible element 45 melts under the effect of excessive temperature, thecam 44 can become inserted into the space freed by the melting of thefusible element 45, thus allowing the ball 43 to disengage. The piston39 is thus unlocked. It can move in terms of translation along the axis40 under the action of the springs 41 and 42. FIG. 17 depicts thethermal cut-out 36 after action of the springs 41 and 42.

Stops 46 and 47 limit the translational movement of the piston 39 withrespect to the sleeve 38. The stop 46 belongs to the sleeve 38 and thestop 47 belongs to the piston 39. These stops 46 and 47 come intocontact under the action of the springs 41 and 42 after the thermalcut-out 36 has been triggered.

The triggering of the thermal cut-out 36 is irreversible and thecoupling device cannot be reengaged without human intervention withinthe device, which intervention consists, for example, in replacing orresetting the thermal cut-out 36.

FIG. 18 depicts an exemplary embodiment of the teeth of the dog clutch.FIG. 18 is a developed view just like FIGS. 3, 6, 9, 12 and 15. Thecrests of the teeth 10 and 11 in this instance are chamfered. This makesreengagement easier, which reengagement can be achieved regardless ofthe relative angular position of the shafts 2 and 3, about the axis 1.Other shapes of the teeth 10 and 11 also allow reengagement to befacilitated. By way of example, it is possible to produce the sides ofthe teeth 10 and 11 in a curve in the form of an involute to a circle.

1. A device for coupling two shafts intended to rotate with respect to acasing about an axis comprising: a dog clutch allowing one of the shaftsto drive the other and clutch-release means allowing the dog clutch tobe uncoupled, characterized in that the clutch-release means comprise aramp secured to the casing, the ramp having a helical shape around thoaxis, a flat disk secured to the first shaft the plane of which issubstantially perpendicular to the axis, an element intended to rollbetween the ramp and the disk so as to cause a translational movement ofthe first shaft with respect to the casing more or less along the axis,the translational movement allowing the dog clutch to be uncoupled. 2.The device as claimed in claim 1, wherein the element intended to rollis a ball.
 3. The device as claimed in claim 1, wherein the shape of theramp allows the element to rotate through about one revolution about theaxis during the clutch-release operation.
 4. The device as claimed inclaim 1, further comprising first means for keeping the element pressedagainst the ramp in the clutch-engaged position.
 5. The device asclaimed in claim 4, wherein the first means ensure that there is afunctional clearance between the element and the disk.
 6. The device asclaimed in claim 4, wherein, at the start of clutch release, the firstmeans move the element to bring it into contact with the disk and withthe ramp.
 7. The device as claimed in claim 6, further comprising secondmeans for controlling the movement of the first means which movementallows the element to be moved.
 8. The device as claimed in claim 7,wherein the second means comprise electromagnetic third means.
 9. Thedevice as claimed in claim 7, wherein the second means comprise athermal cut-out.
 10. The device as claimed in claim 1, wherein saiddevise has a stop to halt the rolling of the element at the end ofclutch release.
 11. The device as claimed in claim 5, wherein, at thestart of clutch release, the first means move the element to bring itinto contact with the disk and with the ramp.
 12. The device as claimedin claim 8, wherein the second means comprise a thermal cut-out.